As the old standard TV technology (CRT) has nearly reached its limits, some new display panels (LCD, PDP, OLED, DMD, . . . ) are encountering a growing interest from manufacturers. Indeed, these technologies now make it possible to achieve real flat colour panels with very limited depth.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, the new technologies have to provide a picture quality as good or better than the standard CRT TV technology. On the one hand, these new technologies give the possibility of flat screens, of attractive thickness, but on the other hand, they generate new kinds of artefacts, which could reduce the picture quality. Most of these artefacts are different as for CRT-TV pictures and so more visible since people are used to seeing old TV artefacts unconsciously.
One of these artefacts is due to the different time responses of the three different luminous materials for the RGB colours used in the panel. This difference generates a coloured trail behind and in front the bright objects moving on a dark background mainly (or the opposite). In case of a plasma display panel (PDP), this artefact is known as “phosphor lag” effect.
FIG. 1 shows a simulation of such a phosphor lag effect on a natural scene with a movement basically in the vertical direction. There is a coloured trail at the edge of the dark background and the white trouser.
On a plasma panel, the red, green and blue luminous elements (also named phosphors while not necessarily having the chemical element P) do not have the same properties because of the chemical properties of each phosphor. In addition the life duration and the brightness are privileged at the expense of behaviour homogeneity. Measurements show that the green phosphor is the slowest, the blue one is the fastest and the red one is mostly in-between. Thus, behind a white object in motion, there is a yellow-green trail, and in front a blue area, as illustrated in FIG. 2.
One known solution from the former patent application FR 0010922 of Thomson multimedia is to compensate the coloured trail while modifying the blue component in the temporal domain.
The phosphor lag problem mainly appears on strong edges of an object in motion, especially on bright to dark transitions or the opposite. In the case of plasma display panels (PDP), the result is a kind of yellowish trail behind each bright to dark transition and a blue area in front of it. This is a result of the difference in the time responses of the phosphors.